MERA PUBLICATIONS. 

No. 2. 



The Scientific and Economic 

Aspects of the 

Cornish Pilchard Fishery. 



2— The Plankton of the Inshore Waters in 1913 
considered in relation to the Fishery. 



By HAROLD SWITHINBANK, 

Fellow of the Royal Society of Edinburgh, 

and G. E. SULLEN. 



ST. ALBANS PRESS. 
1914. 



Monograph 



' ^'iV 



FOREWORD. 

In placing the following paper before the notice 
of those interested in Marine Biology the writers 
desire it to be understood that the present contri- 
bution forms the second of a series of pamphlets to 
appear at irregular intervals. The subjects to be 
dealt with relate largely to the scientific and eco- 
nomic aspect of certain fisheries, together with 
phases of Marine Bionomics having more or less 
connection therewith. 

Applications for copies of the present paper may 
be addressed to G. E. Bullen, The Hertfordshire 
Museum, St. Albans. 



MERA PUBLICATIONS. 

No. 2. 



The Scientific and Economic 

Aspects of the 

Cornish Pilchard Fishery. 



2.— The Plankton of the Inshore Waters in 1913 
considered in relation to the Fishery. 



By HAROLD SWITHINBANK, 

Fellow of the Royal Society of Edinburgh, 

and G. E. SULLEN. 



ST. ALBANS PRESS, 
1914 






Gift 

Aviihnr 

AU5 ' ■'SI'* 



The Scientific and Economic Aspects 
of the Cornish Pilchard Fishery. 



2 — The Plankton of the Inshore Waters in 1913 considered in 
relation to the Fishery. 



By Harold SwithiKbank, f.r.s.r., and G. E. Bullen. 



Methods and Data. 

The observations upon which the following researches are 
founded were taken from the s.s. Mera, R.Y.S. during two 
cruises in the Summer of 19 13. The original scheme of work 
was planned with a view to determining what contrasts existed 
in the plankton environment (a) between the principal fishing 
areas, e.g., Mevagissev Bav, Mounts Bay and St. Ives Bay. 
and (b) before and after the inshore migration of pilchards 
took place. 

The first of these cruises was undertaken from May 31st 
to June 3rd. Twelve station.s were worked in Mevagissey and 
St. Austell's Bays (see Chart .No. i), eleven in Mounts Bay 
(see Chart No. 2), and six in St. Ives Bay (see Chart No. 3). 
Certain full speed tow-nettings were also taken between inter- 
mediate points. The positions of the several stations, together 
with surface temperature and other details, are shown in the 
following table (Table No. i). 



THE SCIENTIFIC AND ECONOMIC ASPECTS 



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OF THE CORNISH PILCHARD FISHERY. 



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6 THE SCIENTIFIC AND ECONOMIC ASPECTS 

The second series of observations were obtained from 
August 20th — 27th, but in view of the then existent condition 
of the fishery, certain material modifications were made upon 
the original scheme of work. The full number of stations was 
worked in St. Ives Bay ; a detour was made to obtain observa- 
tions at three positions in St. Mary's Sound, Scilly ; the number 
of stations in Mounts Bay and Mevagissey Bay was reduced, 
but full speed tovv^-nettings were taken covering a large part 
of the unworked area ; and a series of full speed tow-nettings 
were taken to a position 50° 23' N. x 1° 57' W. (roughly 
eleven miles S. of St. Albans Head). 

At each of the stations, surface tow-nettings of five minutes' 
duration were taken with the fine and medium nets. The nets 
used were of the ordinary open type, constructed of Swiss 
bolting silk of two sizes of mesh, the fine (A) embodying 70 
holes per i cm., and the medium (C) 18 holes per i cm., the 
average length of a hole being .056 cm., and the average 
breadth .036 cm. At several positions oblique hauls, from 
bottom to surface, were made, but as the analyses of these 
samples were not found to differ materially in composition to 
those taken at the surface, they have not been included in the 
tables. The contents of the net were filtered through a net- 
bag of fine silk and preserved immediately in 5 per cent, 
formalin. 

In the determination of the samples, a general examination 
was first made under low magnification, the phytoplankton 
being subsequently submitted to critical treatment, under cover 
slip, with higher powers, i.e., x 600 to x 800. In view of the 
fact that many of the developmental forms of metazoa, and 
certain of the more minute crustaceans occur more frequently 
in the fine net, it has been deemed advisable to combine the 
analyses of both nets under a single column for each station. 
The comparative signs are those adopted in the International 
Plankton Investigations. But as it is impossible, by the 
examination of these symbols, to gain any exact idea of the 
actual bulk of a sample, the quantity of plankton taken was 
measured, after five minutes sedimentation, in a ccm. glass, 
and the results are shown in the next table (Table No. 2). 



OF THE CORNISH PILCHARD FISHERY. 



Table No. II. 
Table Showing Volume of Plankton Collected by Each Haul. 



2nd Cruise. 



Mevagissey 



Lizard to Fowey 

MountsBaySt lOtoL 
Mounts Bay 



Mounts Bay to Scilly 
Scill'y 

S. Ives Bay 



1 

2 

3 

i 

5 

6 

7 

8 

9 

10 

11 

12 

1 

2 

izard 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
] 
2 
1 
2 
3 
1 
2 
3 
4 
5 
6 



Polperro to S. 
Head 



Albans 



I yuancittes. 

■| F. S. 
A Net. C Net.] Net. 
C.Cm. C.Cm. C Cm 



40 
30 
60 
45 
80 
135 
10 5 
60 
5 5 
80 
4 5 
90 



50 
55 
50 
11 5 
80 
95 
7-5 
7 
7 5 
10 5 
150 



13 5 

85 

6 5 

85 

100 

155 



35 

30 
20 
1 5 
20 
35 
25 
7 
4-5 
50 
10 
05 



40 

10 

15 

14 5 

34 5 

7 5 
65 
4-5 

8 5 
9-5 

125 



30 

3 5 
30 
2-75 

4 
30 



Duration of liaul 
F. S, 

CNet, 
Mins. 



A Net 
Mins. 



Net. 
Mins. 



Quantities. 



A Net. 
C.Cm. 


CNet. 
C.Cm. 


80 


3-5 


50 


35 


12-5 


120 


40 


2 5 


60 


20 


10 5 


10 


50 
16 


60 

7-5 


275 


160 


75 


60 


185 

260 
0-5 
05 
1 5 
0-5 
1 5 
05 


31-5 

24 

26-5 

05 

1-0 

4 5 

3-5 

25 

0-5 



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Net. 

C.Cm 



Duration oC haul. | 
F. S 
ANet. C Net. 
Mins 



Min. 
5 



12 5 
12 5 
6-5 



22-5 
23 



Ntt. 
Mins 



40 
40 
40 



70 
70 



105 

15 

14 

16 5 

17 5 
5 

10 5 



30 



8 THE SCIENTIFIC AND ECONOMIC ASPECTS 

The writers do not desire to throw particular emphasis upon 
the value of this method of showing" the extent of the product 
of each net for several reasons, the chief being- the highly 
collapsible nature of certain organisms, notably Phaeocystis, 
when submitted to the action of a preservative, especially when 
it is stated that these determinations were made some weeks 
after the samples had been preserved. 

Yet, with this method of treatment in view, the tow-nettings 
in every instance were accurately timed, and the samples are 
therefore to a certain extent comparable. When, as may be 
seen from the plankton tables, a general similarity in character 
exists between a series of samples, the simple process of add- 
ing- together the figures for each net gives some indication of 
the sporadic distribution of the plankton generally, and a 
comparison of the two, taken in conjunction with a critical 
examination of the analyses, may enable the reader to gain 
some impression of the preponderance of phyto- over zoo- 
plankton, or vice versa. ^ 

Further, it may be stated that, in order to render the results 
of the analyses as nearly comparable as possible, the survey 
of each area was carried out in daylight. 

The surface temperatures were obtained with a Centigrade 
thermometer by Negretti and Zambra (Ivew Tested) for hydro- 
graphical work; the water samples were collected in bottles 
fitted with rubber corks (402. capacity), and were tritrated at 
the Plymouth Marine Laboratory by Mr. C. W. Frost within 
one month of delivery. The soundings were partly taken with 
a Lucas sounding machine, whilst others {i.e., those marked in 
fathoms) are from the Admiralty Charts. 



1 The authors desire to emphasize their full appreciation of the g-eneral 
recommendations with regard to plankton work contained in Appendix iv. 
of the I St Rep. of the Advisory Committee on Fishery Research, but more 
especially that clause regarding the estimation of plankton. The wording 
of this section is as follows: — "It is desirable that a special investigation 
should be at once set up by the Board (of Agriculture and Fisheries) in order 
to elaborate if possible a chemical or physical method for more rapidly 
estimating plankton or the organic matter of plankton in a given sample of 
water. Such a method, if evolved, would be of great value and would save 
much time, etc." 



of the cornish pilchard fishery. 9 

The Plankton of Mevagissey and St. Austell's Bays. 

An examination of the plankton tables (Tables Nos. 3 and 
4), so far as they relate to the Mevagissey area, does not show 
that any remarkable changes had taken place in the composi- 
tion of the plankton during the period intervening between 
the two cruises. It is important to note, however, that the 
diatom flora has become. materially reduced in variety, as might 
be expected, by the end of August. In June the bulk of the 
phytoplankton was composed of the diatoms Rhizosolenia 
alata and R. seniisfina, together with Ceratium fusiis. In 
August both of these diatoms had become comparatively 
scarce, their place being taken by the allied species 
R. Stolterfothi. But it is worthy of note that this latter species 
occurred in very sporadic abundance, rising from " rare " to 
"very common," a fact which is further demonstrated by the 
volumetric measurements. 

From the tables, however, it will be seen that the sporadic 
distribution of individual species of phytoplankton is not so 
generally marked as it is in the case of the zooplankton. Thus 
in the June cruise, it is not difficult to trace the occurrence of 
surface shoals of Acartia Claiisi and Temora loiigicornis, 
together with others of greater frequency composed of Zoeas, 
which in the present series were observed chiefly in the 
Megalopa stage. The samples taken on the first cruise, more- 
over, gave some indication of the interest which was forth- 
coming throughout nearly all the series, from the presence of 
a large and interesting variety of Peridiniales. Thus at 
Stations i, 5 and 12 examples of Ceratunn candelahrnin were 
observed; at Stations i, 3 and 9 C. horndmn; and at several 
positions C . hexacanthum. 

Considered, however, from the food standpoint, the 
plankton did not appear to offer much attraction to drift fish. 
Reference to the volumetric measurements (Table No. 2) shows 
that throughout the entire area the product of the fine net was 
almost invariably greater than that of the medium, on both 
cruises ; and in the light of our examinations it would appear 
that this disparity was attributable to a heavy preponderance 
of phyto- over zooplankton. By adding the products of both 
nets throughout the entire area we get 11 8.5 cc. of material 



lO 



THE SCIENTIFIC AND ECONOMIC ASPECTS 



47" 



46" 45" 



44" 



43" 



42" 



41" 40"nO IF 




MEVAGISSEY and 

ST. AUSTELLS BAYS. 

Roman Numerals = Station Nos. 

Open Circles = Positions. 

Arabic Numerals = Depth in Metres. 



OF THE CORNISH PILCHARD FISHERY. II 

collected at 12 stations on the June cruise, and 70.0 cc. for 
six stations on the August cruise. Reducing these figures to 
common factors we find that the ratio is .84 for the July cruise 
to one for the August, a fact which may possibly indicate some 
increase in the general amount of plankton. 

The Plankton of Mounts Bay. 

As may be seen from the plankton tables, a somewhat 
marked contrast appears to exist in the conditions of this area, 
not only in relation to those of Mevagissey Bay in June, but 
also between the results shown for the two cruises. It will 
be noticed that there is a marked diminution in the variety of 
the protophyta generally in June to that occurring at 
Mevagissey. The bulk of the phytoplankton, however, is still 
composed of the two diatoms previously mentioned, both of 
which on certain positions are reduced to rare and very rare. 
There is certainly a general marked increase in the amount 
of zooplankton, and this is largely due to an abundance of 
Nauplii, together with Evadne nordmanni and Podon inter- 
medium, all of which were chiefly the product of the fine net. 
The generally higher markings against certain Copepods, e.g., 
Acartia Clausi, Cenirofagcs iypicus, and Oithona siniilis are 
additional evidence of this fact. The most interesting feature, 
perhaps, in connection with the samples taken on the June 
cruise was the abundant occurrence of the copepod 
Anotnalocera Pattersoni, at Stations 4, 5 and 6. 

We have already, in a letter to the Editor of " Nature,"^ 
described in general terms the visitation of this species to the 
area under consideration, but an examination of the plankton 
tables will show the restricted extent of the shoal, an idea 
of the density of which may be gained from the tables of 
volumetric measurement. It is to be regretted that the weather 
conditions were unfavourable for any exact visual observa- 
tion, similar to that described by Mr. Matthias Dunn later in 
the year,^ of the colour and appearance of the sea, in the tract 
of water supporting the shoal. 

At the present stage of our investigations, we can 

2 "Nature" No. 2,279, Vol. 91, p. 451. 

3 Vide, "Mera No. i," p. 20. 



12 



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OF THE CORNISH PILCHARD FISHERY. 




14 



THE SCIENTIFIC AND ECONOMIC ASPECTS 





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■rt t; + +iii-++" ii>- + +t:ii^i^it:i 


Table No. IV. 
For po. 




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= .HN«-*OCOr^c6c> i^Oi-lC<»CO'*l/3tDt^COCTSOTHWC*3 
■" J^iHi-H^i-lT-Hr-lrHiHi-li-tCqCNOIO) 



OF THE CORNISH PILCHARD FISHERY. 



15 



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— 1--^ — Lh_' i-iiiiiii-^u i.^ + o + v,iioiy + o itry+ii 1 


i^ — ;!.'''''- ''^1 ^ < i:^i:t ' 1 i: > i: > + itoo,, , 




— h_h — ''iiik.i.iiit.'-ii t:'-+ + tt;ii'-i^'-^- iiottt 1 


'-'- iiiiiuiii^C^ii u + + + ui:ii^i^^t: t:t:"t:i^ u 


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tiiiii + ii t: + ^+iiiit:iit:t: iio^tt u 


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1.1 i.i-i-iii,iiititt:»- "it + '-+iii-i + i+ i-i+o.'-i- *- 


Protophiia cetera. 

24. Halosphaera viridis, Schmitz. 

25. Trochiscia Clevei, Lemm. .... 
Protozoa et Metazoa varia, 

26. Tintinnopsis campanula, Ehbg. 

27. Cyttarocylis denticulata, Fol. 

28. Muggiaea atlantica, Cunn 

29. Pleurobrachia pileus. Mod 

30. Euphysa aurata, Forbes .... 

31. Margelliura octopunctatum, Sars. . 

32. Obelia nigra, E. T, Browne . , . , 

33. Phialidiura cymbaloideum, E. T. Browne 

34. Sarsia prolifera, M, Sars 

35 Echinodermata, larvae 

36. Annelida, larvae 

37. Sagitta bipunctata Quoy and Gaim 

38. Limacina, retroversa, Flem 

39. Uikopleura dioica, Fol, , . . , 
Crustacea — Copef<oda. 

40. Acartia Clausi, Giesbr. . . . , 

41. Anomalocera Pattersoni, R, Temp. 

42. Calanus finmarchicus, Gunn. 

43. Centropages typicus, Kroyer .... 

44. Corycaeus anglicus, Lubb. .... 

45. Euterpe acutifrons, Dana .... 

46. Metridia lucens, Boeck. .... 

47. Microsetella atlantica, Brady 

48. Oithona sirailis, Claus. .... 
49- ,, plumifera, Baird .... 
50 Paracalanus parvus, Claus 

51. Pseudocalanus elongatus, Boeck . 

52. Temora longicornis, O. F. Muller. 
Crustacea cetera. 

53. Caradidae, larvae 

54. Cirripedia, larvae 

55. Nauplii 

56. Evadne Nordmanni, Loven .... 

57. Podon intermedius, Lilljeb 

58. Zoeae ........ 

Pisces. 

59. Ova and Larvae ...... 



i6 



THE SCIENTIFIC AND ECONOMIC ASPECTS 





t?5 


c 
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KOg 



OF THE CORNISH PILCHARD FISHERY. 1 7 

hardly think that this copepod plays any important part 
in the diet of the pilchard in English waters, but 
we take into consideration the statement of the late 
Mr. Matthias Dunn* to the effect that he had observed 
the stomachs of fish, fresuniably arriving from deep 
water, containing large numbers of Anomalocera. The 
following remarks upon the occurrence of the species by 
Prof. G. O. Sars,' moreover, would seem to indicate that an 
occasional abundant occurrence of the species in inshore 
waters would afford ideal food conditions for drift fishes. This 
author states : — " I have met with this form in several places, 
both off the south and west coasts of Norway, generally con- 
gregated in great shoals. The true habitat of this form, how- 
ever, is undoubtedly the open ocean, and it is only after heavy 
gales, and by the accompanying strong sea currents, that it 
is occasionally brought close to the shores and into the fjords. 
. . . Off the west coast of Norway, where it is known to the 
fishermen as ' Blaaaate' (blue bait), its presence in the fjords 
is a very good sign of the approach of the summer herring." 

So far as the area under consideration is concerned, we 
can find no previous record of an inshore visitation of the 
species in large numbers, and an examination of the plankton 
tables published in the International Bulletins shows that the 
species has hitherto been generally recorded in comparative 
frequency only at the extreme western stations (Nos. E4, E5). 

It is perhaps worthy of record that a fair number of young 
fish were taken with the coarse tow-net on the same positions 
at which Anomalocera was very abundant, and these upon 
examination proved to be Motella sp. ranging in length from 
7 m.m. to 19.5 m.m., Amniodytes sp. from 8.5 m.m. to ig m.m., 
and Clupea ? Jiarcngus 18 m.m. (one only). We dissected out 
the stomach contents of several of the rocklings, and found 
that they consisted chiefly of Acartia Clausi, Calanus 
finmarchicus, Centropages typicus, Nauplii, etc., in many 
cases in an intact condition, but in no instance were we enabled 
to detect the remains of Anomalocera. 

■• Dunn, M., " Migrations and Habits of the Pilchards," Lectures on 
Fishes, etc., County Fisheries Exhibition, Truro, iSg3, p. 15Q, etc. 

' * Sars, ,G. C, " An account of the Crustacea of Norway," Vol. iv., 
" Copepoda," p. 140. 



1 8 THE SCIENTIFIC AND ECONOMIC ASPECTS 

Passing now to a consideration of the plankton taken on 
the August cruise, we observe a similar change in the diatom 
flora to that already noted in the case of the Mevagissey area, 
namely, the general decadence of the two species, Rhisosolenia 
alata and R. seniisfina, and an increase in the growth of 
Rhisosolenia Stolterfothi. The condition of this last named 
species, moreover, is somewhat remarkable, occurring as it did 
in very sporadic abundance. Thus, at Stations 3 and 5, and 
in the full speed netting between Stations i and 5, it was met 
with in such profusion that the nets became choked after a 
short immersion in the water, the product appearing as a dense 
glairy mass, whilst at Stations 2 and 6 the species occurred 
in an almost negligible quantity, and at the outer Station 
(No. 10) there was a considerable diminution. In the samples 
taken to the west of Mounts Bay and in St. Mary's Sound, 
Scilly, the species was practically non-existent. 

With regard to the Peridiniales, an examination of the 
tables shows a general increase in certain species, notably 
C eratiurn fusus,hexacanihum, and tripos, Diplofsalis lenticula, 
etc., though it will be noticed that the heavier gatherings of 
C. fiisus and tripos were taken by the full speed net to the 
east and west of Mounts Bay, and at the Scillies. With 
Ceratium hexacanthum and longipes, reference to the tables 
will show that their distribution was not so marked in the 
extreme western area as it was in Mevagissey Bay and the 
adjacent waters. The comparatively close inshore occurrence 
of Dinophysis tripos between the Lizard and Fowey, west of 
Mounts Bay, and at the Scillies, is also a matter deserving of 
comment. 

In the case of the zooplankton generally, the tables of 
volumetric measurement show more clearly than do the plank- 
ton tables the contrast existing between the samples taken in 
Mounts Bay and those from the Scillies. In both areas it 
will be seen that the predominant species are the Copepods 
Centropages typicits, Oithona siinilis and Temora longicornis, 
but that in St. Mary's Sound, Scilly, the samples were of a 
much richer character; an important feature when the contem- 
porary condition of the fishery is considered. 



OF THE CORNISH PILCHARD FISHERY. 



19 




ST. IVES BAY. 



Roman Numerals = Station Nos 

Open Circles = Positions. 

Arabic Numerals = Depth in Metres. 



!k 



The Plankton of St. Ives Bay. 

But few features of interest appear to exist between the 
composition of the plankton observed at the several stations 
in St. Ives Bay on both cruises, but generally speaking the 
contrast between the samples taken on the first cruise and those 
of the second is somewhat remarkable. In June, as it may 
be seen from the plankton tables, the whole of St. Ives Bay 
was literally choked with Phaeocystis globosa, to such an 
extent in fact that the contents of a bottle filled over the 



20 THE SCIENTIFIC AND ECONOMIC ASPECTS 

ship's side appeared to be composed entirely of the species, 
amongst which a few zoeas seemed to struggle for existence. 
We do not maintain that the analyses of the samples can 
give the reader a just appreciation of the actual composition 
of the plankton, in view of the fact that both the fine and 
coarse nets undoubtedly ceased to filter after a very short 
immersion. The chief point of interest which we have to 
consider, therefore, lies solely in the fact of the profusion of 
this flagellate in St. Ives Bay, whilst it appears to have been 
entirely absent from Mounts Bay. It is well known that 
Phaeocystis globosa is a neritic species, belonging to the 
so-called "periodic plankton," and as its term of vegetation 
is comparatively short, it was a matter of no remark to find 
that, on our second visit to St. Ives Bay in August, it had 
entirely disappeared. Yet an examination of the volumetric 
measurements of the samples taken in August shows that the 
quantity of plankton generally existent in this area, after the 
passing of the Phaeocystis, was very slight indeed. A dis- 
cussion upon the causes of this phenomenon : as to whether 
Phaeocystis crowds other forms of the plankton out of 
existence by its rapid propagation, or in its decay renders the 
water insupportable for a time to other organisms, etc., is 
beyond the province of this paper. 

Apart from Phaeocystis, the general composition of the 
rest of the plankton, so far as it was possible to judge under 
the deterrent influence to which we have already referred, i.e., 
the clogging of the nets, appeared in June to present several 
features in common with those observed in Mounts Bay. For 
example, the two diatoms, Rhizosolenia alata and R. semis- 
fina, again make their appearance in varying abundance at 
the several stations, and the two Copepods, Acartia Clausi 
and Oithona similis, are also fairly well represented. In the 
August cruise, however, the substitution of Rhizosolenia 
Stolterfothi for the two allied species already mentioned was 
not observed. The only point of some interest in connection 
with the zooplankton was the occurrence of Anomalocera 
Pattersoni at five of the stations. This copepod was repre- 
sented, however, solely by zmadtdi individuals of the species. 



of the cornish pilchard fishery. 21 

General Considerations upon the Plankton of the 
Cornish Inshore Waters. 

In considering the condition of the plankton observed as 
occurring throughout the several areas studied, together with 
certain other facts, we find that there is some evidence to 
show that an abnormal influence was at work during 19 13. As 
to whether this condition had existed to any extent in 191 2 
it is impossible to determine ; but, if we associate possible cause 
with now well known effect, and attribute the extreme eastern 
migratory movement of pilchards in 19 13 to such abnormal 
influence, we have also to take into consideration the state- 
ments of fishermen at Brighton to the effect that pilchards were 
taken there regularly, in small numbers, during 191 2. Thus, 
if one might be permitted to speculate upon these facts, it 
would seem possible to suggest that in 19 13 these conditions 
had become sufficiently pronounced to bring about an effect 
so marked as to engage attention. 

But we have now to consider in detail such evidence as 
we hold lending support to our theorv so far as it affects 
the year 1913. Unfortunately the only previous observations 
which have a more or less direct bearing upon the area under 
consideration are those taken in connection with an investiga- 
tion upon the mackereP in 1906-7, together with others taken 
throughout a greater number of years upon the International 
Plankton Cruises at Station £.7,' which, it is to be regretted, 
is situated at some distance outside Mounts Bay. 

With such slender evidence of the planktonic conditions 
existent in former years it is impossible to do very much in 
the way of comparison, but certain facts are too obviously of 
importance to be overlooked. 

We have already remarked upon the abundance and variety 
of the Peridiniales occurring in the plankton samples. With 
regard to Ceratitim hexacanthiim, we can find no observation 
of its abundant occurrence in the Channel, other than that of 



6 Vide Bullen, G. E., "Plankton Studies in relation to the Western 
Mackerel Fishery." 

"^ Vide Plankton Tables, " Bulletins de Conseil International pour 
rExplgration de la Her." 



22 THE SCIENTIFIC AND ECONOMIC ASPECTS 

Gough* in 1903, who recorded it for the south-western area 
alone and only in February and November. From the 
plankton tables it will be seen that this species occurred in 
comparative scarcity at Mevagissey in June, increasing some- 
what in abundance and extending its distribution to the Scillies 
in August. In view of the fact that the species appears to 
be an oceanic one, its greater abundance in the full speed 
nettings which were taken on the run of the ship's course well 
out to sea, would suggest that it occurred in some profusion 
outside the close inshore waters of Mounts Bay and the 
adjacent area. 

It is important, moreover, to note the sporadic abundance 
of Diflof sails lenticida in August, and the occurrence of 
Peridineum divergens, Dinophysis tripos, Microsetella 
atlantica, Oithona plmnifera, and Limaclna ? retroversa, to 
understand that in the coastal waters we have observed certain 
forms which have generally hitherto been associated with the 
plankton of the extreme western area of the English Channel. 
In this connection, moreover, it may be mentioned that Gough" 
states that Anomalocera Paitersoni may be regarded as a 
species generally occurring in the Great West Bay. We thus 
have some evidence to show that the plankton of the areas 
under consideration was of an abnormal character, and in the 
nature of its composition lending support to a theory that 
extreme western biological conditions were existent further to 
the east than in certain former years. Certain other facts are 
before us, which might possibly lend some support to a still 
wider view of the matter than that which we have already 
indicated. We refer more particularly to the occasional visita- 
tions of shoals of Physalia, which extended to our personal 
knowledge as far east as Studland toward the end of May. 

Salinities of Water Samples. 

The analyses of the water samples taken within the area 
under consideration, and the absence of similar observations 
derived from Mid Channel and elsewhere however lend no 

8 Gough, L. H., " Rep. of the Plankton of the English Channel in 1903," 
p. 333 Int. Inv. Mar. Biolog. Ass. Rep. I. 

9 Op. cit., p. 335. 



OF THE CORNISH PILCHARD FISHERY. 23 

useful evidence in support of the above theory. For it will 
be seen, on reference to the salinity table (Table No. i), that 
no remarkably high salinities occur at any position. On the 
May cruise the highest figures are 35.12 for the extreme 
southern and eastern stations (Stations Nos. 9, 10) in Mounts 
Bay, and 35.18 for two positions in St. Ives Bay. In 
Mevagissey and St. Austell's Bays there is a drop to 33.31, 
rising to 33.74 in the three extreme eastern stations (Stations 
Nos. I, 2, 12), a moderate constancy ranging from 34.6 to 
34.7 obtaining farther to the west. 

On the second cruise in August the salinities recorded 
throughout the entire coastal area vary only in the second 
place of decimals, from 35.02 to 35.08. The samples taken 
in St. Ives Bay are very nearly similar inter se, but generally 
very slightly higher than those of Mounts Bay and the 
Mevagissey area. A contrast certainly does exist between 
these samples generally and those taken in St. Mary's Sound, 
which show an increase to 35.2 ; a fact which, when it is remem- 
bered that the samples were taken in enclosed coastal waters, 
may possibly indicate the presence of water of higher salinity 
in the comparatively near vicinity. From the above observa- 
tions, it is obviously impossible to draw any definite conclu- 
sions ; but, when considered in the light of what is already 
known regarding the physical conditions of the Channel,'" 
some importance has necessarily to be given to such a material 
increase within a radius of 50'. 

The Plankton of the Eastern Area. 

It is to be regretted that circumstances precluded a more 
thorough investigation of the planktonic conditions existent to 
the east of what hitherto has been regarded as the pilchard 
fishery area, and that the observations, such as they are, con- 
sisting solely of full speed tow-nettings, were not continued 
up to the Straits of Dover. For, lacking as they do the full 
value of samples taken by the ordinary tow-net at regular 
stations, the gatherings of plankton taken between Polperro 

w Vide Matthews, D. J.j " Rep. on the Physical of the English Channel 
in 1913," and other subsequent papers. 



24 THE SCIENTIFIC AND ECONOMIC ASPECTS 

and St. Albans Head afford many points of interest, and lend 
much valuable support to the general considerations upon food 
conditions. We have to consider the bathymetrical rise and 
fall of certain species, the long distance covered by each haul 
(about five miles), in which it was possible to run through one 
or more shoals of various organisms, together with several 
other important points, in making any comparison between 
these samples and others taken in the western area. But the 
examination of the analyses shows at least one very important 
point, namely, that phytoplankton gradually decreases to a 
minimum from west to east of the course covered, and that 
what we may justly regard as desirable food species increase 
in abundance. The seven hauls comprising the present series 
are comparable inter se solely in length of duration (thirty 
minutes each), and for the reasons previously stated it is 
obviously impossible to draw any exact deductions. Yet from 
the evidence afforded by the volumetric measurements of 
samples Nos. 2 and 6 taken almost at the extreme western 
and eastern points, it would seem possible to suggest 
that throughout the area covered the distribution of the 
plankton generally was very sporadic. The appearance in 
comparative abundance of that most important food species, 
Calanus finmarchicus, in the eastern area, hitherto noted in 
comparative scarcity in the coastal waters of the west, is another 
matter of some importance. But, in comparing roughly the 
last five samples with the two full speed nettings taken from 
Scilly to Mounts Bay earlier in the cruise, we find that the 
actual volume of material is somewhat higher for the former ;" 
and in view of the fact that this plankton consisted almost 
entirely of animal matter, we have some evidence to show that 
the richer feeding grounds lay to the east of Plymouth. 



11 Note. — Our method of comparison has consisted in adding together 
the total volume of (a) the five last samples of the eastern series and (b) the 
two western (Scilly-Mounts Bay), dividing each product by the total number 
of minutes occupied in the collection of each. The comparable figures gained 
in this way are 325 western, 383 eastern. When it is noticed that one sample 
of the latter series consisted only of 0.5 c.cm. of material it will be seen that 
the contrast is not without some significance. 



of the cornish pilchard fishery. 25 

The Condition of the Pilchard Fishery considered in 

RELATION TO THE PlANKTON. 

In a previous paper'- it has been shown that an intimate 
correlation appears to exist between the plankton environment 
of inshore waters and the extent of migration. It was naturally 
to be expected that the quantity and suitability of the food 
supply should constitute what, in the present state of our 
knowledge, certainly appears to be the predominant factor in 
a profitable fishery. For it has never been suggested that the 
pilchard moves into inshore waters for any other purpose than 
that of seeking; suitable feeding- grounds. 

Cunningham'" has described the pilchard as being the most 
truly marine clupeoid frequenting the coastal waters of Great 
Britain; and it is a well-known fact that the species, unlike 
certain of its congeners, habitually spawns at some distance 
from land. 

That the family trait of seeking brackish, or even fresh 
water, occasionally manifests itself, however, is evidenced by 
the now well-established fact that pilchards may often be 
taken in the Fowey river as far inland as Lostwithiel.'^ Yet 
upon occasional instances of this character we can adduce no 
useful evidence to show that the pilchard seeks the coastal 
waters fro!?i necessity. It is well known that the fish forming 
the subject of the Cornish fishery are for the greater part in 
either unripe or " shotten " condition (shirmers), and in this 
respect the pilchard may be compared with the small immature 
mackerel which move into coastal waters, after the advent of 
the spring shoals. In considering the migrations of pilchard, 
therefore, we are probably discussing movements which are 
undertaken for no other reason than that of feeding. Yet in 
making this statement we do not desire to be too definite, since 
in dealing with a species whose near allies seek fresh water 
for the important purpose of spawning — a species, moreover, 
which occasionally seeks similar habitat itself — it is impossible 
to say whether an atavistic tendency may not be in evidence. 



12 "Mera No. i." 

13 Cunning-ham, J. P., "Mark. Mar. Fishes." 

1-* Teste Mr. Moses Dunn, of Fowey, and several other local observers. 



26 THE SCIENTIFIC AND ECONOMIC ASPECTS 

On the coast of France, Portugal and elsewhere, where the 
sardine industry is prosecuted, the success of the fishery is 
well known to depend largely upon what may be termed the 
caprice of the fish in appearing at certain stations at more or 
less regular seasons. The uncertainty of this fishery alone 
appears to afford some evidence in support of a theory that 
inshore migration is determined largely by the attraction 
afforded by the coastal waters from the food standpoint. Yet, 
bearing in mind the normal delimitation of range of the species, 
we have also to place important consideration upon sea 
temperature and salinity. 

It is not hard to believe that if physical conditions approxi- 
mating to those existent in the normal habitat of the pilchard 
were to extend beyond their usual limits, and that the fish in 
migration found no suitable food supply awaiting them in their 
usual summer haunts, that migration might be extended farther 
afield within the area exhibiting suitability of habitat from the 
phenological aspect. 

We have already summarized the somewhat scanty direct 
evidence at our disposal, showing that certain planktonic 
conditions, usually associated with the extreme western area 
of the Channel, were existent in the coastal waters of Cornwall 
during the summer of 1913. The meteorological observations^'' 
for the south coast of England in the same season show air 
temperatures generally above the mean for July, August and 
September, and our own observations tend to show a general 
surface water temperature distinctly above the normal. The 
visitations of Physalia and certain other forms of Mediter- 
ranean fauna had also been noted. So much for the evidence 
supporting a theory of the extension of suitability of habitat. 

With regard to the unsuitability of the food supply existent 
in the coastal waters of Cornwall, we may refer briefly to the 
high proportion of phytoplankton over zooplankton in 
Mevagissey Bay, St. Austell's Bay and Mounts Bay, the 
literally choked condition of St. Ives Bay in June, due to 
Phaeocysth, and the extreme poverty of the plankton remain- 
ing there in August. And when we compare these conditions 

15 Vide Appendices to the " Daily Weather Reports " of the Meteorological 
Office. 



OF THE CORNISH PILCHARD FISHERY. 27 

with those existing farther to the east, and in the Scillies, we 
find that suitable food conditions certainly did not exist in 
the usual summer fishery area. 

Summarizing briefly the condition of the fishery, we find 
in the effect some remarkable evidence in support of the 
probable cause upon the lines which we have already indi- 
cated. It is now a well-known fact that the migratory move- 
ments of pilchards extended as far east as Deal. From 
information derived from fishermen at Brighton, it appeared 
that regular catches of some thousands had been made a few 
miles off the coast in the adjacent waters and up to the Straits 
of Dover, throughout the latter half of July, in August, and 
well into September. It may be mentioned that we examined 
the stomach contents of fish taken off Brighton in September, 
and found that they consisted largely of zoeas and certain 
Calanoid Copepods, notably Calamis finiuarchicus, Centro- 
fages typicus, etc. — food of a character which we have often 
met with in fish from the western area in former years. During 
the months when pilchards, the catches of but a few drifters, 
were being marketed regularly at Brighton and elsewhere 
under the fictitious name of "herring," and one firm at Deal'" 
were accumulating as a " by-product " over five hundred barrels 
of fish cured as " bloaters," the Mevagissey and Mounts Bay 
fishermen were securing slender catches of but a few hundreds 
per night. In the Scillies, however, where something in the 
nature of an experimental fishery was being carried on, chiefly 
by men who had little previous experience of drifting, the 
fish appeared to be present on the ground in sufficient quantity. 

It was not until the beginnmg of October,^'' that the Mounts 
Bay fishery became in any way productive ; and it is a signifi- 
cant fact that this change was practically contemporaneous 
with an observed inshore visitation of a large shoal of the two 
Copepods AnomaloceraPattersom 2,ndCalamis finmarchicusP 

In an important paper on the mackerel, Dr. E. J. Allen" 



16 Teste Mr. Matthias Dunn, of Newlyu. 

1" Vide " Mera No. i," p. 20. 

18 Vide " Mera No. i," id. loc. 

13 Vide .A.llen, E. J., "Mackerel and Sunshine." 



28 THE SCIENTIFIC AND ECONOMIC ASPECTS 

has tentatively shown that some correlation may be found to 
exist between the productiveness of the fishery, and the extent 
of bright sunshine occurring in the early spring months, prior 
to the fishing season. This author states, " Experiments on 
the cultivation of marine plankton diatoms in the laboratory, 
upon which I had been engaged, had drawn my attention to 
the great importance to be attached to the intensity of light to 
which the diatoms were exposed. It therefore occurred to me 
that a special abundance of Copepods during the month of 
May might be due to a special amount of sunshine during the 
earlier months of the year, which would increase the amount 
of phytoplankton, the Copepod food. An attempt was there- 
fore made to correlate the average quantity of mackerel per 
boat taken in May with the number of hours of bright sunshine 
recorded during the first quarter of the year." 

The observations upon which this paper is founded appear 
to leave little doubt in the mind of the reader that, under what 
we may term ideal conditions, such a correlation probably does 
invariably exist, but under the present inadequate system of 
hshing by the majority within a comparatively confined area, 
the official statistics of landings, as the author justly points 
out, lend but little support to such a theory. For as one of 
the present authors has already shown,-" a superabundance of 
phytoplankton in coastal waters appears to correlate with a 
poor mackerel fishery, and to a large extent the findings in 
this and a previous paper (Mera No. i) indicate that the same 
may hold good in the case of the pilchard. It follows that we 
have to go beyond the limits of the area aft'ected by the majority 
of the fishermen, in those years when phytoplankton is 
abundant in the coastal waters, to find evidence of the more 
exact working of this cycle of events. For as it now stands, 
a superabundance of phytoplankton in coastal waters, food of 
a character unsuitable to the fish themselves, appears to form 
a powerful factor in the delimitation of the extent of inshore 
migration. It follows that it is necessary that this vegetable 
plankton be consumed largely by the zooplankton before the 
fish are induced to approach in appreciable numbers to the 

2» Bullen, G. E., "Plankton Studies," p. zSi. 



OF THE CORNISH PILCHARD FISHERY. 29 

inshore waters. A productive fishery, carried on within the 
comparatively narrow Hmits of the coastal waters, as is usual, 
appears to be based on a very finely adjusted cycle of physical 
and biological conditions, in which an extremely narrow margin 
is allowed for any abnormal condition, arising from the pre- 
ponderance or paucity of one or other of the given elements. 
The general results of the present season's work, there- 
fore, tend in every way to support the deductions advanced 
in a previous paper ;-^ but, although at this early stage of our 
investigations it is obviously impossible to define with any 
degree of certainty the probable causes governing the extent 
of migration of pilchard to the coastal waters of Great Britain, 
a consideration of the abnormal conditions of 19 13 afford a 
basis of argument, such as might not have been forthcoming 
from a study of a succession of normal seasons. 

Briefly to summarise these considerations, therefore, we 
find :— 

(i) That certain biological conditions, which may usually 
be associated with the extreme south western area of the 
English Channel, were observed in the coastal waters of the 
Cornish fishery area; a fact which might lend support to a 
theory of an extension of suitable habitat for pilchards. 

(2) That in the same region phytoplankton, i.e., food 
of a character undesirable to the fish, preponderated over 
zooplankton throughout the greater part of the season. 

(3) That in Scilly, and to the east of Plymouth, food 
of an eminently desirable character was largely in evidence. 

Passing now to the facts concerning the fishery, we find : — 

(4) That the migration of pilchards extended as far east 
as Deal, and that a profitable fishery was carried on within 
the near vicinity. 

(5) That the fishery was also of a productive character in 
Scilly. 

(6) And that it was not until an observed coastal visitation 
of shoals of Calanoid copepods to the waters of Mounts Bay 
early in October that the Cornish fishery became productive. 

21 "Mera No. i." 



30 THE SCIENTIFIC AND ECONOMIC ASPECTS 

The above facts, considered conjointly, obviously lend 
some support to a theory that the pilchard seeking coastal 
waters, prompted thereto possibly by some obscure atavistic 
tendency, may, if suitable feeding grounds be not afforded by 
the waters in the immediate vicinity to its winter habitat, and 
providing that suitable conditions of sea temperature, salinity 
and density exist elsewhere, extend its migration beyond 
normal limits until a desirable feeding ground is encountered. 



APPENDIX I. 



The Occurrence of Sexually Mature Pilchards in 
Inshore Waters. 

As previously stated in the foregoing paper, the pilchard 
habitually spawns at a considerable distance from land, the 
tish forming the object of the Cornish drift fishery are therefore 
either in unripe condition, or of the type known as " shirmers," 
i.e., spent fish of somewhat emaciated appearance and above 
the usual size. Cunningham'" remarks upon the fact that ripe 
pilchards are generally taken accidentally in mackerel nets 
shot twenty to forty miles from land, the catch seldom exceed- 
ing fifty. The period of time over which such fish are taken 
extends from the beginning of June to the end of October; 
they are commonest in July and August. The same author 
comments upon the comparative scarcity of ripe males caught 
in this manner, but omits to mention any exact data as to the 
usual area from which such examples were derived, beyond 
detailing one specific instance of the collection of eggs on 
September 5th, 1893, ten miles south of the Eddystone. 

All of our records prior to 19 13 of the capture of spawning 
pilchards in mackerel nets lie on positions twenty to thirty 
miles south to south-west of the Wolf, and they are not 
numerous. 

From information derived from a fish curer at Newlyn, it 
appeared that a catch of five hundred ripe pilchards was made 



OF THE CORNISH PILCHARD FISHERY. 3 1 

by a drifter shooting for mackerel about ten miles south of 
the Lizard early in June (19 13). The same observer men- 
tioned that he had dealt with a catch of about two thousand 
in July, and that fish of this character had been very frequently 
through his hands prior to the end of August. These facts 
appeared to have impressed themselves on his memory more 
particularly owing to the difficulty he had experienced in 
getting the fish to cure satisfactorily by the usual method of 
salting. Replying to our further enquiry, he stated that, to the 
best of his belief, the ripe males were in almost even propor- 
tion to the females. 



APPENDIX II. 

Net Curing by Creosote. 

In the "Fish Trades Gazette," Vol. xxxi., No. 1606, 
p. 36, appears an interesting article dealing with the curing of 
herring and pilchard gear by means of "green oil," i.e., crude 
creosote, a practice which has been recently in vogue amongst 
the West Country fishermen. It appears that the majority 
of observers interested in the fishing industry, if not from the 
scientific from the enlightened standpoint, have regarded the 
innovation with considerable misgiving throughout the past 
season. As to how w^ell founded these fears certainly were, 
is proved by the results of a series of experiments performed 
at the Plymouth Marine Laboratory by Dr. E. J. Allen. It 
appears that in a first experiment one part of the oil added 
to 100,000 parts of sea-water, and well shaken up, proved fatal 
to thirty healthy swimming prawns (Hemimysis) within an 
hour. In a further experiment one part of the oil was added 
in a similar manner to 10,000,000 parts of sea-water, and 
twenty-five specimens of the same crustacean were put in. 
One-half were dead in twenty-four hours, three -quarters were 
dead in two days; all were dead in five days. In both experi- 
ments sufficient aeration of the water was provided for, and 
in a control experiment carried out in ordinary sea-water under 
similar conditions of aeration, etc., no deaths occurred. 

?3 Cunningham, J. P., " Mark. Mar. Fishes," p. 170. 



32 ■ THE SCIENTIFIC AND ECONOMIC ASPECTS 

It may perhaps be mentioned that medicinal creosote is 
soluble about one in four hundred of water, but the solubility 
of "green oil," in which guiacol probably predominates over 
creosol, may be considerably less. When, as we have heard 
it described by Mr. Matthias Dunn, a freshly cured net is 
shot and one can see an emanation of creosote floating on 
the surface of the water, it is not hard to understand the natural 
result upon both plankton and fish situated in the near vicinity. 
For even if we do not admit that a toxic effect could be 
produced upon plankton in the open sea by such means, it 
is not hard to believe that the pilchard possesses sufficient 
intelligence to prevent it from driving headlong into con- 
taminated water. 



APPENDIX III. 

Pilchard with Reduplicated Rays to Caudal Fin. 

On August 2oth (19 1 3) we examined at Newlyn a pilchard 
252 m.m. in length, a male, caught two miles S.W. x S. of 
St. Michael's Mount, which exhibited a malformation of a 
type approximating to another which we once before met with 
in a specimen now preserved in the Museum of the Plymouth 
Marine Biological Laboratory. Unfortunately the present 
example was inadvertently destroyed, but referring to our 
notes upon the subject taken at the time, it appears that the 
specimen had a double complement of rays to the caudal fin. 
This characteristic had the effect of broadening the base of 
the tail to about one-half again its normal extent. ■ The fin 
itself was nearly double the width of that of_ an ordinary 
example at its widest part, but appeared naturally to slightly 
overlap upon itself in the centre. The individual rays 
appeared to be generally thicker throughout their entire length 
than is usual. A fisherman, questioned upon the subject, 
stated that he had, very infrequently, met with similar 
examples before. 



002 880 841 




